1. Field of the Invention
The invention pertains to the field of gears. More specifically, the invention pertains to a spur gear that has teeth cut for interfacing with both a worm driver and a rack.
2. Description of Related Art
Gears are toothed wheels used to transmit motion between components of a machine. Spur gears, also known as straight cut gears, are the most common type of gear. These gears, which are used to transmit power between two parallel shafts, have straight teeth parallel to the gear axis. Spur gears are classified as external, internal, or rack and pinion. External spur gears have teeth pointing outward from a center wheel. Internal gears have teeth pointing inward toward the gear axis. A rack and pinion combination transforms rectilinear motion into rotary motion and vice versa. The smaller of two gears is called the pinion. In a rack and pinion gear combination, the wheel is the pinion, because the rack is viewed as having an infinite pitch circle radius.
Worm gears are used to connect nonparallel, nonintersecting shafts at right angles. The worm has a helical tooth (thread) on its surface. The mating gear is the worm wheel. Worm gearing achieves large velocity reductions by using the worm as the driver and the worm wheel as the driven gear. The primary reasons for using industrial worm gearing are (1) to transmit power efficiently, (2) to transmit power at a considerable reduction in velocity, and (3) to provide a considerable mechanical advantage to overcome a comparatively high resisting force.
Due to the different interconnections involved, teeth for a spur gear are shaped differently from teeth for a worm wheel.
Briefly stated, a gear for use as the pinion in a rack and pinion gear includes spur gear teeth that have an upper portion of the face cut in a worm cut so the gear is effective as a worm wheel for a worm gear while retaining involute curved faces so it is effective as the pinion for the rack. The rack, pinion, and worm driver are connected. When the worm gear connected to a shaft, power is transmitted from the shaft to the rack via the worm driver and pinion with all gears making line contact instead of point contact. This improvement turns one gear piece into two gears. The rack pinion can be geared to a worm gear while it is also matched up with a straight cut rack. In this way the gear translates force between the two different types of gears.
According to an embodiment of the invention, a spur gear that interfaces with both a rack and a worm driver includes a wheel and a plurality of teeth spaced around the wheel, wherein each tooth includes opposing faces cut in a shaped curve such that the shaped curve satisfies the fundamental law of gear tooth action; an upper portion of each face cut in a worm cut; and a top land cut in a worm cut.
According to an embodiment of the invention, a gear combination includes a worm driver, a rack, and a spur gear interconnected between the worm driver and the rack, wherein a plurality of teeth of the spur gear have faces which satisfy the fundamental law of gear tooth action; an upper portion of each face is cut in a worm cut; and each tooth has a top land cut to match the worm driver.
According to an embodiment of the invention, a telescoping valve comprises a rack held in place by guide bushings, a spur gear that meshes with the rack, wherein the spur gear has a top land cut to interface with a worm gear, and wherein upper portions of the face of the spur gear that interfaces with the worm gear are concave cut to match the convex thread sides of the worm gear, and the worm gear being affixed to a rotating shaft, such that rotating the shaft rotates the worm gear, which in turn meshes with the spur gear, which meshes with the rack, such that power is transmitted from the shaft through to the rack, with all of the gears making line contact instead of point contact.